flat plate equivalent drag area (D/q): 0.45 sqft

I found that at the VmaxProbe page.

How can you define flat plate equivalent area..or do you calculate it ?

I mean do you just add up all the drag and see what it end ups as a flat plate ?

Yes, you sum up the drag from all the different components, such as the wing, tail, and fuselage. Also toss in induced drag, and guess at the amount of cooling and interference between the different components like the wing to fuselage junction.

On paper, it is just a guess. It's not till the airplane is fully tested that better number emerge.

On the origninal design it was thought that it's total drag area would be 0.31 sq. ft. But as the design evolved (retractable gear were eliminated), the drag area went up.

A more interesting question might be why did it crash at the end of the first flight? I believe it was due to vertical stabilizer being mounted inverted under the fuselage to protect the propeller (it was a pusher design). At some angles of attack, I believe that the rudder action would reverse, so when the pilot pushed left, the airplane would respond to the right. The end of the first flight ended with the plane snapping over and crashing inverted killing the pilot.

Hi HighPlains
What plane that crashed are you referring to? Something is missing here.

The airplane called the Vmax Probe. Designed and built by Lars Giertz. It was designed to set a record speed in the lightest FAI category, gross weight of 661 pounds or 300 Kg. It had a wing span of 14 feet, wing area of 28 sq. ft., and a wing loading of just under 24 lbs/sq ft. It was powered by a 3 cylinder 2 stroke engine that was normally rated at 100 hp, and was configured with a pusher prop so to promote laminear flow on as much of the fuselage as possible.

Due to the high wing loading, it's takeoff and landing speed was around 100 mph. At the end of it's first flight it ended up upside down. Lars was not wearing a helmet, since he had made the airplane too small for him to fit inside wearing one. The crash was in 1997, and you can see a photo of the design on the following web page.


http://www.webcamsue.nl/vmax.html

Thanks High Plains !


I understand the flat plate area tells AC designer a lot about the drag without having to go into details.

May I ask how do you know so much about the VmaxProbe ?

Do you know the plane in my avatar ?


rgds,

Juke

Why did it crash ?


My educated guess is :

With 70 flying hours ( with high performance prop plane and 40 minutes in a BD-5 ) mr. Giertz was not the best test pilot for the plane he himself called a "rascal".

He radioed of temperature rise to 230 F and came in for a landing in 5 minutes after take off.

Stall speed was 80 mph ( or kts ? ) and plane has very high attitude position of the tail on the ground and no flaps.


My speculation:

He may have caught in the ground effect and kept on going at high speed ( due to no virtually drag of the airframe )and to reduce speed he throttled to idle and prop started to twist the plane near 90 mph and to compensate this this he gave opposite aileron and lost lift of the wing due to the NFL414F re area 10 000 000 foil was only performing well in slightly faster speeds.

The prop that was a wooden fixed one was optimized to go 300 mph and was almost biger than the elevator stab.

I don't know what plane your avitar is, it looks a lot like a Sierra Sportplane S-1. I had been following the Probe design for about a year before the crash. He had been blogging on the development for quite a while before. For instance, he said that this was the second one of the airplanes he built, as the first one was in a land fill.

There was also a rather extensive write-up (9 or 10 pages) in a book written by Bruce Carmichael, called "Personal Aircraft Drag Reduction" published in 1996. He calculated a complete build-up of the drag for the design. While there are truly countless numbers of books on wings, very few books look at the rest of the airplane since it is so difficult to quantify.

Yeah it is Sierra Sue..you got it right.

http://en.wikipedia.org/wiki/Drag_coefficient

I am buzzled...how do you add up all the drag...if the wing is laminar flow type and plate the drag coefficient is 0.001...what is it if the foil is 12% thick ( 0.0047-0.0045 in AR-5 ) ?

AR-5 pages Carmichael say the drag coefficient of the plane was 0.016...when he says the wing drag area is 0.248 sq ft ( in the summary )...does he mean flat plate equivalent area ? Because the frontal area of the wing is at least 15 x that area. http://www.ar-5.com/condrag94.html

How much in % is the interference drag generally in a smooth plane ( 4.1% in AR-5 and induced drag 3.6 %) ?

-

Seems to me that in the wing he is using wetted area and multiply that with coeffiecient and in the fuse and multiply that area by coefficient.

The frontal area of the wing does not matter one bit. You do take the area and multiply by the Cd. For fuselage, it is the wetted area. However, if you assume that part of the flow on the fuselage is laminar, then that portion has a different number than the part with turbulent flow.

At one time it was thought that it was not possible to have laminar flow on a fuselage with a tractor engine, but later studies showed that between pulses of turbulant air from the prop, that the flow could revert to laminar.

I found the same thing working with water cooled power transistors, it is very hard to maintain turbulant flow in the water channel. While you want laminar flow on aircraft, it is a very bad thing if you want to transfer heat.

The interference drag between the wing and fuselage, or the fuselage and tail surfaces is generally assumed to be between 5 to 10% of the combined wing and fuselage drag, and the tail interference to add another 10% of the tail surface drag. All a guess. Cooling drag is usually significant too, with most light planes rather dirty. That can add 10 to 15% more drag to a design. Even air leaks into the airplane's cockpit adds drag.

Thanks HP,


This explained a lot to me ( and stydying 3 hours the AR-5 page ).

I wonder if Lars Giertz died due to lack of oxygen...I saw no inlet to get fresh air into cockpit...did you ?


regards,

Juke

How do I convert that 0.880 sq ft drag of AR-5 into flat plate equivalent area ?

0.88 sq. ft. is the equivalent flat plate area for the AR-5. That is the sum of the total drag.

A nomograph that relates hp, speed, and flat plate drag is useful.

Use a prop efficiency of 80 to 85%.

But Tom Aberle's new prop has 92% efficiency...I rather use that. Look for the thread in www.aafo.com about Phantom.

Thanks for the nomograph.

I doubt the accuracy of the claim.

Sorry High Planes the story was in another thread ( Could sound barrier be broken with a prop plane ? ).

http://www.eaa.org/experimenter/arti...02_elippse.asp

Insert: Testing of the fixed-pitch, three-blade ELIPPSE prop on my Lancair shows that it is performing at 82 percent efficiency in a climb at 105 mph IAS and at least 90 percent efficiency in cruise at 200 mph TAS.

90 % it says at TAS 200 mph.

I have no doubt that he believes he has achieved 90%, but there are many possibilities for measurement errors. And I really doubt he has done glide tests with the airplane to find out it's flat plate drag.

Finally, is he trying to sell something?

I was talking to a testpilot and he said the underside rudder is good but if you come in a tailslide the effect indeed is reversed in that kinda rudder. I immediately increased the upper side component of the rudder stab area on my design and made the underside rudder lower and thicker + longer ( wider ).

http://www.absoluteastronomy.com/topics/Bede_BD-5

Bede 5b all 4 short winged versions crashed ( due to high landing speeds )...a snapping was a tendency of that kite due to high centerline of thrust.